Donald Trump is poised for sweeping nationwide wins on Super Tuesday, solidifying his position as the Republican front-runner and intensifying the pressure on his struggling primary rivals to find a way forward.

Top Republicans — including governors who convened an emergency conference call on Monday on which Trump was Topic A — expect the real estate mogul to carry as many as 10 states on Tuesday night, an outcome that would deal a body blow to Texas Sen. Ted Cruz, who has staked his campaign heavily on the Southern states holding nominating contests, and to Florida Sen. Marco Rubio, who has yet to win a primary and isn’t expected to do so on Tuesday.

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“If Trump wins 8 or more states on Tuesday, it would take a massive collapse on his and/or his campaign’s part for him not to be the nominee,” said Tony Fabrizio, a longtime GOP pollster and strategist who advised Rand Paul.

Trump’s march to the nomination has set off a wave of anxiety across the Republican Party establishment as top officials weigh whether to endorse him — or denounce him as anathema to the party's values. Reflecting that angst, on Monday morning, New Mexico Gov. Susana Martinez and Wisconsin Gov. Scott Walker, the heads of the Republican Governors Association, convened fellow governors for an unusual conference call to discuss how the primary was unfolding — and Trump was a central topic of conversation.

At one point during Monday’s call, which lasted around 30 minutes, Kentucky Gov. Matt Bevin asked New Jersey Gov. Chris Christie to discuss last week’s bombshell decision to back Trump. According to two sources familiar with the call, Christie mounted a detailed defense of his endorsement, explaining that he’d known the real estate executive for over a decade and had grown confident in his ability to lead the country.

The stakes on Tuesday are perhaps highest for Cruz, who had once hoped to establish a stranglehold on Super Tuesday, carefully tailoring his evangelical image to the conservative states that are voting that day and campaigning heavily in towns throughout Tennessee and Oklahoma. He has described March 1 as the most important day of the Republican primary calendar.

Yet, with Trump rampaging throughout the South, it’s now possible that Cruz will only emerge with a win in his home state of Texas, a contest the senator has begun likening to the Alamo. Trump has made deep inroads into Cruz’s evangelical base, portraying himself as a steadfast Christian while casting Cruz as “the single biggest liar I’ve ever seen.” Jerry Falwell Jr., an influential evangelical leader and Trump supporter, has recorded a robo-call for the Trump campaign which is being sent to households throughout Virginia. In the call, Falwell, the president of Liberty University, tears into Cruz and accuses him – four times – of using “dirty tricks.”

“Politicians can’t wait to tell us about their values, but I care more about the choices they make when no one is looking,” Falwell says in the call. “Ambition must never be a substitute for character. Please vote for Donald Trump.”

The Cruz campaign has not yet released its post-Super Tuesday schedule. But in the immediate days ahead, Cruz is likely to campaign heavily in a trio of deeply conservative states – Idaho, Louisiana, and Kansas – that hold their nominating contests over the next week.

Rubio, meanwhile, will immediately pivot to his home state of Florida, where he will spend much of his time ahead of the do-or-die March 15 primary. With polls showing him badly trailing Trump, Rubio is expected to launch an all-out effort to win the state, where a defeat could be fatal. His top aides have vowed in unequivocal terms that they will not lose Florida, which awards its 99 delegates on a winner-take-all basis.

Rubio’s planning for the Florida primary has been long in the works. He recently dispatched Clint Reed, a former Republican National Committee political director, to Florida help guide his efforts to secure his home state, according to two sources familiar with the move. Reed also played key roles for Rubio in Iowa and South Carolina.

Rubio’s aides are convening top donors to a national finance meeting to coincide with the March 9 debate in Miami. On March 10 and March 11, he will embark on a fundraising tour that will take him to Palm Beach, Naples, and Ocean Reef. One of the events will be held at the home of Gerald and Darlene Jordan, prominent South Florida socialites who were major benefactors to Mitt Romney’s 2012 campaign.

No matter what happens on Tuesday, Cruz and Rubio’s allies point out, Trump will be nowhere close to securing the 1,237 delegates needed to secure the GOP nomination. The 595 delegates up for grabs will be distributed proportionately, meaning that Cruz and Rubio are expected to rack up a substantial number even if they do not succeed in winning many states. Going into Super Tuesday, Trump has won 82 of the 133 delegates that have been awarded so far.

That means the primary race could well go on for weeks or months longer without any candidate meeting the threshold for securing the nomination.

“Donald Trump is the clear front-runner, and he’s in a very strong position,” said Steve Munisteri, a former Texas Republican chairman who has closely studied the delegate allocation process. “But it’s not over.”

Yet there’s little question that the structural dynamics of the primary favor Trump. Assuming he wins most of the states voting on Super Tuesday and his rivals choose to stay in the contest, Trump will be the beneficiary of two major advantages: a lead in the delegate count, and a splintered Republican field.

With Rubio likely to be blown out on Tuesday, his allies are latching on to the notion that he could still keep Trump from amassing a majority of delegates and then win over party insiders at the convention in Cleveland, securing the nomination at the 11th hour.

“There is a very narrow way forward,” conceded Mel Martinez, a former Republican National Committee chairman and past Florida senator who endorsed Rubio on Monday.

But, Martinez said, there was hope. A majority of the party, he argued, found Trump “increasingly unpalatable,” and they would resist him.

“How that manifests itself I don’t know, but I believe there is a sense by many, myself included, that he just cannot be the nominee,” he said. “So a convention scenario could begin to develop.”

Speaking to reporters on Monday, Cruz ridiculed the idea. “All these crazy voters go one way, we’ll step in with all of our money and anoint our white knight to ride in and save the day … That’s not going to happen.”

The growing ranks of forces looking for ways to stop Trump insist they haven’t lost hope. Our Principles PAC, an anti-Trump super PAC being overseen by former Mitt Romney aide Katie Packer, has launched an aggressive fundraising campaign and is eyeing the possibility of launching ad campaigns against him in four delegate-rich states voting in March: Michigan, Missouri, Illinois, and Florida.

The group, which has tapped veteran Republican strategist Ed Goeas to conduct polling, has secured donations by a number of prominent Republican Party contributors, including Marlene Ricketts, part of the family that owns the Chicago Cubs, and Stan Hubbard, a broadcasting executive.

“I don’t think the opposition to Trump is going quietly into the night anytime soon,” said Josh Holmes, a former chief of staff to Senate Majority Leader Mitch McConnell. “The vast majority of Republicans are horribly dissatisfied with the current state of affairs and there is no sign whatsoever that fundraising or energy is dissipating for an alternative.”

Some in Rubio’s campaign have privately expressed their frustration that prominent members of the party establishment have yet to gravitate to him. While Romney and Jeb Bush have been loud critics of Trump, neither has endorsed the Florida senator – nods that would open up veins of fundraising dollars and help Rubio consolidate the party around him.

While many of Bush’s backers have announced their support for Rubio since the former Florida governor dropped out of the race, others have remained on the sidelines.

One top Bush donor — Mel Sembler, a Florida real estate developer and former ambassador to Italy – declined in an email exchange to say whether he’d support Rubio. He said he was focused on defeating a medical marijuana initiative and “recovering from Jeb’s withdrawal.”

A few Bush backers are throwing their support elsewhere. In a telephone interview on Monday, Doug Ose, a wealthy former Republican member of Congress who fundraised for Bush, said he was endorsing Trump. Ose, who represented California’s Central Valley for three terms and hails from the mainstream wing of the GOP, said he viewed Trump as a problem solver and that he’d been turned off by what he described as the increasingly negative tone of Rubio’s campaign.

“I actually think Senator Rubio 10 years from now is going to be our guy,” the former congressman said. “I hope he doesn’t do damage to himself.”